Not applicable.
The present invention relates to a spray nozzle.
Various forms of agricultural spray nozzles are known. In each, a liquid such as a fertiliser or pesticide is supplied to the spray nozzle. The spray nozzle breaks up the liquid into droplets on exiting through an outlet provided in the spray nozzle tip. The spray nozzles may produce various different spray patterns, such as a flat spray pattern, a xe2x80x9csolidxe2x80x9d cone of drops, a xe2x80x9chollowxe2x80x9d cone of drops, etc.
Various spray nozzles have been produced which attempt to provide a better dispersion of the liquid being sprayed in order to reduce the amount of liquid used per unit area of crop in order both to keep down costs and also to minimise any adverse effect on the environment.
In the spray nozzle marketed by the present applicant as xe2x80x9cTurboDrop,xe2x80x9d a flow of liquid through the spray nozzle passes through a venturi restriction which causes air to be entrained with the liquid flow, the air being drawn in through an air inlet in the side of the spray nozzle assembly. The liquid and entrained air pass into a relatively long mixing chamber. The liquid and air mix and air-filled droplets form when the mixed liquid and air pass out through the spray tip in a selected spray pattern. The air-filled droplets tend to drift much less than droplets produced by conventional spray apparatus and provide excellent coverage of an area.
A similar device is disclosed in GB-A-2256817 in which liquid passes into a convergent inlet end of a venturi in the spray nozzle, there being a gas inlet to that convergent inlet end of the venturi. The venturi itself is relatively long and passes to a so-called mixing chamber though it is understood that mixing will take place in the venturi as well as in the mixing chamber itself.
In each of these prior art spray nozzles, each of which relies on the venturi effect, the venturi or mixing chamber has to be relatively long in order to ensure that sufficient mixing of the liquid with the entrained air is achieved to allow turbulence to be created so as to provide air-filled liquid droplets. The venturi/mixing chamber also has to be long in order to prevent liquid passing straight out of the nozzle; in other words, there must be sufficient time for mixing to occur before liquid exits the spray nozzle. This means that these prior art spray nozzles as a whole are long.
The length of the prior art spray nozzles is a problem in the field because the spray nozzles are mounted on booms that are either carried by or towed by a tractor, for example. Such booms are usually folded for storage or and for transit between spraying areas. The long prior art spray nozzles are easily knocked off when the booms are folded.
Moreover, it is usually recommended to use a liquid supply pressure of typically 7 bar (approximately 700 kPa) for some of the prior art spray nozzles. Such high pressures (compared to a typical value of 3 bar (approximately 300 kPa) for conventional spray nozzles) require expensive powerful pumps. Such high pressures can also cause damage to the spray components that incorporate the spray nozzle assembly. Moreover, the long mixing chambers/venturi make these prior art spray nozzles difficult to clean. This is compounded by the fact that, in practice, such spray nozzles will typically be covered in mud as a result of having been carried behind a tractor.
Another type of prior art spray nozzle is a so-called twin fluid nozzle. A liquid is forced into a mixing and atomising chamber in the spray nozzle and typically strikes a plate provided within the chamber. Pressurised air is forced into the chamber to carry the liquid out of the chamber outlet to a spray nozzle outlet where the liquid atomises and droplets issue as a spray. It should be noted that the air is forced into the chamber in a twin fluid nozzle rather than being drawn in by movement of liquid through the chamber as in a venturi nozzle. Examples of twin fluid nozzles are disclosed in EP-A-0225193, GB-A-2157591, WO-A-96/20790 and U.S. Pat. No. 4,828,182.
According to a preferred embodiment of the present invention, the present spray nozzle comprises a pre-chamber and a mixing region, a first inlet defining a first fluid flow path for admittance of a first fluid to the pre-chamber, a second inlet defining a second fluid flow path that is crossed by the first fluid flow path for admittance of a second fluid to the pre-chamber, a wall between the pre-chamber and the mixing region and having an aperture therethrough coaxial with the first fluid flow path, and an outlet from the mixing region through which fluid can pass from the mixing region out of the spray nozzle. The outlet does not lie on either the first or second fluid flow paths, such that in use a first fluid entering through the first inlet mixes with a second fluid entering through the second inlet in the mixing region before the mixed first and second fluids passing out through the outlet.
The aperture in the wall between the pre-chamber and the mixing region allows fluid to pass from the pre-chamber to the mixing region, while the wall itself tends to prevent fluid in the mixing region passing back to and out of the second inlet. In the preferred embodiment, the wall defines the pre-chamber positioned upstream of the mixing region and into which the first and second inlets open. In a venturi nozzle where air is drawn in as the second fluid through the second inlet, the size of the aperture in the wall can be adjustable to allow some degree of control over the amount of air that is drawn in through the second inlet. The pre-chamber helps to keep down the overall length of the nozzle by promoting more efficient mixing of the first and second fluids.
A first end of the second inlet is preferably open to atmosphere and a second end of the second inlet preferably opens to a position adjacent the first fluid flow path, whereby passage of a first fluid through the first inlet causes air to be drawn in through the second inlet.
Alternatively, there may be means for connecting the second inlet to a supply of pressurised air.
The spray nozzle may have a wall opposite the first inlet and transverse to the first fluid flow path, with the wall having an aperture defining the outlet that is offset from the first fluid flow path. The aperture of the wall between the pre-chamber and the mixing region preferably has a cross-sectional area that is greater than the cross-sectional area of the first inlet.
The first inlet preferably includes two first inlet apertures. In this embodiment, the wall between the pre-chamber and the mixing region preferably has two apertures therethrough, which are respectively coaxial with the two first inlet apertures. The use of two inlet apertures helps to ensure that the pattern of fluid exiting the outlet in use is symmetrical, ensuring more uniform coverage during spraying. The inlet apertures are preferably symmetrically spaced either side of a central longitudinal axis of the spray nozzle.
The second fluid flow path is preferably perpendicular to the first fluid flow path. The second inlet preferably comprises two second inlet apertures.
The outlet may lie on a central longitudinal axis of the spray nozzle.
The spray nozzle is preferably provided in two parts, the first part having the first and second inlets, the second part having the outlet. The use of two parts means that the size of the outlet can be altered easily by using a different outlet part having a different size outlet. The use of two parts also facilitates cleaning of the nozzle.
According to a second aspect of the present invention, there is provided a method of spraying using a spray nozzle having a pre-chamber and a mixing region, a first inlet defining a liquid flow path for admittance of a liquid to the pre-chamber, a second inlet defining an air flow path that is crossed by the liquid flow path for admittance of air to the pre-chamber, a wall between the pre-chamber and the mixing region and having an aperture therethrough coaxial with the liquid flow path, and an outlet from the mixing region, through which mixed liquid and air can pass from the mixing region out of the spray nozzle. Again, the outlet preferably does not lie on the liquid and air flow paths. The method comprises the steps of passing a liquid through the liquid inlet, mixing said liquid with air entering through the second inlet in the mixing region, and passing mixed liquid and air out through the outlet.